In recent years, as an air conditioning system for a data center, attention is paid to an outside air cooling system utilizing outside air.
For example, an outside air cooling system is available wherein the temperature of outside air taken in is adjusted by a temperature adjustment apparatus to generate cold air and the generated cold air blows out from the floor side into a space at one side of a rack row while warm air exhausted into a space at the other side of the rack row is exhausted to the outside from the ceiling side. Then, the warm air is circulated to the temperature adjustment apparatus, or an air conditioner is provided over the space at the one side of the rack row toward which cold air is blown up such that the temperature of the warm air is adjusted to generate cold air and the generated cold air is supplied into the space at the one side of the rack row.
Further, for example, also an outside air cooling system is available wherein an air conditioning room and a server room are provided in a data center, and, when the temperature of outside air is high, outside air taken in is cooled by the air conditioning room and supplied into the server room, but when the temperature of outside air is low, outside air taken in is supplied as it is into the server room. Further, when the temperature of outside air is excessively low, part of warm air to be exhausted to the outside is sometimes returned to the air conditioning room such that it is mixed with outside air and supplied into the server room.